There are many applications in which a flexible elongate element such as a line or conduit requires sealing at an interface between two environments between which there is a high pressure differential. The boundary may be constituted by a bulkhead at which the sealing must be performed. The element may, for example, be an optical fibre for monitoring conditions on one side of the boundary. Another example is a fine tube used for capillary sampling of material on one side of the boundary.
It is particularly important to provide highly reliable seals for such elements at interfaces in many different applications, for example the chemical and food processing and nuclear industries, in which the consequences of leakage of fluid past the seal can be severe.
Another field in which the reliability of seals is very important is that of undersea telecommunication elements, for example optical fibres, in which stretches of telecommunication cable are interrupted by repeaters at which the signal in the fibres is boosted. The seal between the fibre and the repeater housing must be designed to withstand the extreme pressures at considerable depths for a projected life time of 25 years or more.
Sealing glands are known for undersea optical communication fibres which comprise a metallised fibre soldered into a cylindrical body screwed into a bulkhead flange and also an electrode embedded in insulating ceramics also screwed into bulk head flange for power feed connections. In both cases the gland assembly comes as a unit with approximately 1 meter lengths of fibre sealed in place which are spliced to the fibres of the incoming cable, on one side, and to the receiving fibres inside the repeater housing, on the other.
In both cases, the gland comprises a tubular arrangement extending out of the housing in line with the cable. The radial thickness of the arrangement is considerable in comparison with the cable to be sealed in order for it to be strong enough to withstand the pressures at depth. It is also made long enough in order to provide sufficient sealing contact between the sealing material and both the cable and the housing. Both of these factors have to be taken into account when designing the housing and can necessitate a more bulky housing shape than would otherwise be the case.